This proposal deals with a study of modifications of the translational system which occur in the dimorphic fungus, Mucor racemosus. These changes, which occur in tRNA and in the RNA and proteins of ribosomes, are roughly correlated with the yeast to hypha transition which takes place when the chemical environment of the organism is altered. Mucor racemosus, a phycomycete, is heterothallic, it can be grown in chemically defined media, and the morphogenetic transition can be completely controlled by several different manipulations. The goals of this study are two-fold: a) to define in precise chemical terms the changes which we have observed in components of the translational system, and b) to learn whether the alterations are causally related to the morphogenetic process. The proposal deals specifically with studies on (1) the nature of changes in methylated bases of ribosomal RNA, (2) the control and enzymology of the phosphorylation of a protein in the 40S ribosomal subunit, and (3) the chemistry and enzymology of modifications in specific transfer RNAs.